The use of implanted medical devices, while critical to many treatment modalities, is associated with undesirable infections. Approximately 60,000 deaths in the United States occur annually from device-related, hospital-acquired (nosocomial) infections. In the United States, bacterial infections from medical devices cause 9 to 11 million infections and 87,500 to 350,000 deaths per year. Urinary catheters alone cause more than 500,000 urinary tract infections per year. A 10-year study by the Centers for Disease Control (CDC) found a 7% incidence of nosocomial infections among all U.S. hospital admissions and even higher rates internationally. Each year, there are an estimated 2 million nosocomial infections in the United States and an estimated 3 million in Europe.
Many current infection control methods rely upon the use of antibiotics; however, these methods are problematic due to the natural ability of many microbes to develop resistance against existing antibiotics. According to the CDC, the “last line of antibiotic defense has been breached.” Therefore, there exists a need for effective non-antibiotic infection control technologies to reduce the estimated $6.5 billion annual cost associated with nosocomial infections in the United States. There is great a need to prevent infection resulting from the use of medical devices that are inserted into the body of a patient, such as devices used for localized delivery of biologically active materials to the body of a patient, or during intravenous delivery of fluids or medications to the body of a patient. Patients that will benefit the most from such devices and methods for their use are those at the highest risk for blood infection and death.
A number of devices are available in the art for providing an antimicrobial environment or antimicrobial properties for insertable medical devices. Currently there are present in the art various patents describing medical devices whose surfaces can be covered with antimicrobial agents. For example, U.S. Pat. No. 5,344,411 to Domb et al. discloses an anti-infective coating bound to the surface of a catheter or other medical device. The catheter is coated with solutions of an antimicrobial agent and water and is allowed to dry. The water on the catheter then evaporates, leaving an anti-infective coating on its surface. What remains is a medical device whose surface is left directly coated with an antimicrobial agent.
Also in the art are various coating compositions and methods for coating medical devices. For example, U.S. Pat. No. 5,001,009 to Whitbourne discloses a method for coating a substrate such as a medical device with coatings, comprising applying each solution to the substrate surface and then evaporating it at an elevated temperature. In U.S. Pat. No. 6,387,080 to Rodsten discloses a method for forming an osmolality promoting hydrophilic coating on the surface of a medical device such as a catheter.
However, medical devices whose surfaces are charged or coated with antimicrobial agents can exhibit a risk of leeching, leaking and migration of the antimicrobial agent away from the portion of the device that requires the antimicrobial agent. The terms “leeching,” “leaking” and “migration” are used to describe the movement of the antimicrobial agent away from a portion of the medical device that should include the antimicrobial agent. One of the portions of the medical device that requires an antimicrobial agent is the portion that is located in proximity of the point of entry of the medical device into the patient's body. It is desirable for an antimicrobial agent to be located in the proximity of the point of entry of the medical device so that microbes that can cause infections can be killed off or prevented from entering the body. Leeching, leaking or migration of the antimicrobial agent can lead to a reduced concentration of the antimicrobial agent in the portion of the medical device that is in proximity to the point of entry of the medical device. Therefore, there is a risk of diminished antimicrobial effect at the point where such an effect is needed the most. Such reduction in effectiveness results in a higher risk of infection, as well as higher costs and an unnecessary waste of antimicrobial agents.
Therefore, it has been found that the amount of antimicrobial can be used most efficiently if it is somehow concentrated at the point where it can be the most useful for preventing infection. U.S. Pat. No. 5,049,140 to Brenner et al. discloses a catheter with an antimicrobial fitting that can be cut into a plurality of pieces and attached at fixed distances along the length of the catheter. The fittings are fabricated from a heavy rubber elastomer (with a Shore A hardness of between 80 and 95) and are fixed permanently onto the length of the catheter.
U.S. Pat. Nos. 5,236,422 and 5,505,695 to Eplett describe cuffs for urinary catheters, wherein only the cuffs themselves are charged with an antimicrobial agent. These cuffs are inserted into the body of the patient (through the urethra) as a means for preventing infection from bacteria migrating along the length of a urinary catheter inside the body of the patient. However, these cuffs are fully inserted into the body of the patient, rather than being attached on the device at a point external to and proximate of the point of entry of the medical device. The cuffs described in those two patents are placed completely inside the urethra, and their antimicrobial effect is concentrated at the internal point of insertion of the catheter into the patient's body. There are drawbacks to putting the cuff into the body of the patient. Locating the cuff completely inside the body is not desirable because it may expose internal body tissues to infection. It is also often more painful for the patient, and may require a larger incision and therefore a heightened likelihood of infection at the point of entry.
Also present in the art are devices, such as those described in U.S. Pat. No. 5,686,096 to Khan et al., in which an antimicrobially charged device comprises a resilient pad that is attached to the skin of the patient. The pad, which contains an antimicrobial agent, has at least one void for receiving a catheter. The pad is affixed to the skin of the patient by the use of an adhesive. Such adhesives are a drawback because they can irritate the skin.
Therefore, there is a need for medical devices or components of medical devices that can provide adequate antimicrobial protection from infections and that also avoid leaking or migration of the antimicrobial agent from the portion of the medical device that should include the antimicrobial agent.